Lens

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What is the Lens?

Lenses are magnifying glasses with curved sides. A lens maybe a piece of transparent glass that concentrates or disperses light rays when it passes through them by refraction. Due to the magnifying property, lenses are utilized in telescopes and other magnifying devices. Lens are employed in cameras for gathering the sunshine rays. In cameras, not one, but a group of lenses is used for the gathering of sunshine. Magnification of a lens is the relation between the dimensions of the image formed and also the size of the item. Lenses may be employed in groups to avoid the blurriness or distortion caused to the image formed by the lens.


Related Terms

  • Centre of Curvature

A lens has two spherical surfaces. These two spherical surfaces form part of a sphere. The centre of those spheres is understood because of the centre of curvature.

  • Principle Axis

The Principal axis can be defined as an imaginary line that passes through two centres of curvature which are known as the optic axis.

  • Optical Center

The centre point of a lens is termed as the optical centre of a lens. The optical centre is sometimes denoted by O.

  • Aperture

The effective diameter of the circular outline of a spherical lens is termed as the aperture of the lens.

  • Focus

Focus is the point onto which collimated light parallel to the axis is targeted.


Types of Lenses

Today, we've different types of lenses. Generally, they're either categorized as a simple lens or a compound lens. A simple lens could be a single piece of magnifying material while a compound lens includes a variety of simple lenses arranged along a common axis. Optical aberrations are sometimes found in simple lenses while this property is eliminated in a compound lens. The other benefit of the compound lens is that the magnification of the lens is often adjusted as per the user’s requirements.


Non-spherical Lenses

  • Aspheric Lens

The aspheric lens is usually called a non-spherical lens. An aspheric lens may be a lens whose surface isn't a part of a sphere or a cylinder. The complex surface of an aspheric lens reduces or eliminates optical aberrations as compared to a straightforward lens. One aspheric lens can replace a mix of straightforward lenses leading to a system with much-reduced size.

  • Cylindrical Lens

Cylindrical lenses can be considered as the lenses that have a curvature along only one axis. It converts laser diode elliptical light into a round beam or to focus light into a line as it is one of its main purposes. Motion picture anamorphic lenses are an example of such lenses. 

  • Other Lenses

Lenticular lenses are a group of microlenses that are utilized in lenticular printing. Images produced by this kind of lens have an illusion of depth. 

A bifocal lens consists of two or more focal lengths or either a graduated focal length.

A gradient index lens could also be a lens with flat optical surfaces while an axicon lens features a conical optical surface.

  • Convex Lens

A convex lens could be a lens with an outward curve. Unlike the diverging lens, the thickness at the centre of a lens system is the thickness at the perimeters of the lens. Convex lenses are converging lenses. They need the flexibility to converge a parallel beam of sunshine to some extent. The focus is on the alternative side of the lens from which the sunshine rays originate. A converging lens with one side flat is termed a Plano-convex lens. The lens found within the human eye may be a prime example of a converging lens. 

Another common example of a lens is the simple microscope that's accustomed to correct Hypermetropia or long-sightedness. Convex lenses are employed in cameras as they focus on the sunshine and produce a transparent image. Convex lenses are used in compound lenses that are further used in magnifying devices like microscopes and telescopes.


Did You Know?

The word lens comes from the word ‘lēns’, the Latin name of the lentil because double-convex lenses are lentil-shaped. The Lens culinaris also gives its name to a geometrical figure. Arguably according to certain scholars, many archaeological pieces of evidence indicate that there was widespread use of lenses in the olden age, spanning several millennia. The so-called Nimrud lens may be a quartz artefact dated to the 7th century BC which can or might not be used as a simple microscope or a burning glass. Many experts have also suggested that certain Egyptian hieroglyphs represent "simple glass meniscal lenses".

FAQ (Frequently Asked Questions)

1. What is Spherical Aberration?

One of the first reasons for the occurrence of aberration is because the spherical surfaces of the lens don't seem to be the perfect shape and as a result, although beams are parallel, they are distant from the lens axis. This causes the blurring of the image. Aberration will be corrected by using a normal lens having the proper surface curvatures for a specific application.

2. What is Chromatic Aberration?

Chromatic aberration occurs thanks to dispersion. When it happens, a lens fails to focus on all colours on the identical point of distortion then, in that case, a colourful fringe is observed around the image of that object, it is then fixed using an achromatic doublet (or achromat). There are other sorts of aberrations and some of them include field curvature, astigmatism, barrel, and pincushion distortion. Chromatic aberration causes lens dispersion, with various colours of light travelling at distinct speeds while passing through a lens. As an impact, the image can look blurred or noticeable coloured edges (red, green, blue, yellow, purple, magenta) can appear around objects, specifically in high-contrast situations.